Problem: $J$ $K$ $L$ If: $ JL = 21$, $ KL = 2x + 3$, and $ JK = 9x + 7$, Find $KL$.
From the diagram, we can see that the total length of ${JL}$ is the sum of ${JK}$ and ${KL}$ $ {JK} + {KL} = {JL}$ Substitute in the expressions that were given for each length: $ {9x + 7} + {2x + 3} = {21}$ Combine like terms: $ 11x + 10 = {21}$ Subtract $10$ from both sides: $ 11x = 11$ Divide both sides by $11$ to find $x$ $ x = 1$ Substitute $1$ for $x$ in the expression that was given for $KL$ $ KL = 2({1}) + 3$ Simplify: $ {KL = 2 + 3}$ Simplify to find ${KL}$ : $ {KL = 5}$